The cannabis flowering stage is a crucial moment in the life cycle of this incredible plant. It is a time of transformation, as the once vibrant and verdant vegetative growth gives way to a riot of color and aroma. The buds that develop during this stage are the key to the plant’s future, containing the cannabinoids such as THC and CBD. It is make or break during the flowering stage as to weather your grow is going to be a big yielding, potent harvest or a lack lustre crop of mediocre weed.
Follow our comprehensive guide as we walk you through week-by-week the most important stage of your cannabis plants life. We will highlight any potential pitfalls that you might face and go into granular detail on how you can get the most out of your plants.
What are the first signs of the flowering stage?
The flowering stage is the moment when it starts to get exciting and you can finally see the fruits of your labor come into fruition. The first signs that your plants are visibly transitioning into the flowering stage are the elongation of the internodes, or the space between leaves on the stem. As the plant shifts its focus from vegetative growth to reproductive, the buds will begin to form and the plant will begin to produce the flowers.
As the buds begin to form you should be able to notice that tiny pistils begin to develop around the nodes where the flowers will grow.
Another early indication of flowering is a change in the color of the leaves, which may become slightly yellow or red as the plant redirects energy towards the development of buds. Finally, a distinct, sweet and pungent aroma will begin to emanate from the flowers that begin to grow.
The importance of sexing your cannabis plant
Cannabis pistils are tiny hair-like structures that grow from the flowers (buds) of the female cannabis plant. These pistils play a key role in the reproduction of the plant and are one of the first signs of the sex of a cannabis plant. It is very important that you understand the difference between a male and female plant and what to look out for early on because having a rogue male among your crop could ruin your entire grow.
How to spot a female plant
In the early stages of growth, male and female cannabis plants look similar and it can be difficult to determine their gender. However, as the plants mature, female plants will start to develop pistils, while male plants will develop small clusters of pollen sacs.
The pistils of a female cannabis plant will change color and become more prominent as the plant approaches maturity. They will start off white or cream-colored and gradually turn red, orange, or brown as the plant reaches the flowering stage. This is a clear indicator that the plant is female and capable of producing bud.
How to spot a male plant
On the other hand, male cannabis plants will produce pollen sacs that are filled with pollen. These will eventually burst and release their pollen fertilizing the female plants. It is vital that you remove any male plants from your grow room before they pollinate the female plants. Once this happens, the female plants will stop producing bud and begin producing seeds instead. The resulting harvest will be low potency, poor quality bud that is full of seeds.
What do buds look like as they begin to form?
When cannabis buds start to form, they begin as small, tightly packed clusters of green and white leaves. The buds will be covered in tiny white hairs, which are actually pistils and will be surrounded by resin-coated trichomes. As the buds continue to develop, they grow larger and become dense, filling out and taking on a more rounded shape. The trichomes also increase until they eventually cover the buds in a sticky, glittering layer that gives them a frosty appearance. By the time the buds are ready for harvest, they will be a dense, fragrant mass of green leaves and sticky, resinous trichomes, with the pistils now having changed to a red, orange, or brown color.
Week 1 flowering stage
- Humidity 50 – 60%
- Temperature 75-85°F
- NPK 5-10-7
During the first week of the flowering stage, cannabis plants will continue to grow and develop. Many growers expect a plant to immediately stop growing and begin producing bud, however, during the first week of the flowering stage what often happens is that plants have a last-minute growth spurt known as the ‘flowering stretch’. This is the plants last minute ditch at attempting to outgrow its competitors to get first dibs on the suns energy.
In terms of appearance, your plants will have a bushy and compact appearance, with the growth of new branches and leaves gradually slowing as the energy is diverted towards bud production.
The ideal temperature and humidity in your grow room should be between 70-85°F and 40-60% relative humidity. Sticking to these levels will really help to reduce the risk of mold later on during the flowering stage.
In terms of nutrients, you should provide your plants with a nutrient NPK ratio of around 5-10-7. This is ideal for the early flowering stage, because it supplies a higher level of phosphorus which supports bud development. However, it’s important to note that the specific NPK ratio will depend on the strain you’re growing and the specific nutrient requirements it may have.
Weeks 2-3 flowering stage
- Humidity 50 – 60%
- Temperature 75-85°F
- NPK 5-15-10
During weeks 2 and 3 of the flowering stage, your plants will continue to develop and mature. The stretch seen in the first week of flipping the lights will begin to slow down and the plants will place more emphasis on producing flowers.
It is during around week 2 that you will begin to see the first signs of sex. Female plants will begin to produce pistils, these look like little white hairs and are where the buds will form. Now that you are in week two you can up the nutrients a little and begin a higher dose of phosphorus and potassium by giving a 5-15-10 NPK ratio.
As week 3 approaches your plants will have stopped their ‘flowering stretch’ completely and the plant will start to produce buds at a faster rate. Towards the end of week 3 flowering, you should begin to see larger calyxes form and the first signs of trichomes appearing.
Weeks 3-4 flowering stage
- Humidity 40 – 50%
- Temperature 68-78°F
- NPK 5-15-10
- Use fans to improve airflow
At this stage the plant will have completely stopped growing and 100% of its energy should be on producing bud. The buds will grow and become denser and more compact. You will also notice that they begin to swell and trichomes will continue to spread over the leaves and buds.
Try to maintain a temperature of 68-78°F (20-26°C) with a relative humidity between 40-50%.
It’s important to continue to closely monitor the growth of your plants regularly and make any necessary adjustments to maintain optimal conditions. If any issues arise, such as nutrient deficiencies, mold or pest problems, they need be addressed promptly at this stage to prevent any serious impact to yields.
As your buds grow in size and density you should make sure that your grow room has good airflow. This will prevent air and moisture from becoming stale which can lead to mold. Hopefully you already have an extraction fan in place, but to further improve the airflow in your grow room consider installing a rotating tower fan or two to keep the air moving.
Weeks 4-6 flowering stage
- Humidity 30-40%
- Temperature 68-78°F
- NPK 5-15-10
- Begin light defoliation starting with any dying leaves
By week 5 your plants will be in full on flowering mode and the buds will begin to grow more compact and become covered with white pistils. Towards the end of week 6 you will see that the trichomes have increased in number on the buds and surrounding sugar leaves giving your grow room a strong recognizable cannabis smell.
Towards the end of week 6 you should start inspecting your buds closer up so that you notice the changes. You should see that the calyxes have gotten fatter making the buds bigger and heavier. Any trichomes at this point will be clear in color as the THC has not yet fully developed.
By now some of your stems may begin to turn woody, which can cause them to snap under stress. You should tie any stems that appear to be bending too much to a support to prevent them from snapping. Right now, your plant has diverted almost all of its energy to bud production and you may begin to see some leaves start to yellow. You can carry out some light strategic defoliation of any dying or brown leaves to expose as many bud sites as you can. Do not over trim the leaves, remember the plant still needs lots of energy to fatten up those buds and you need to avoid stress as much as possible at this stage.
Weeks 6-8 flowering stage
- Humidity 30-40%
- Temperature 68-78°F
- NPK 4-10-7
- Leave plants in the dark for 48 hours before harvesting
Week 6, 7 and 8 will be the last flowering weeks for some cannabis plants. At this point your buds should be nice and dense and the pistils that were previously white have darkened turning to an orange, brown color by week 8. You might even see some leaves at the bottom beginning to turn yellow; this is completely normal. Most of these changes are due to excessive growth of buds and the plant funnelling all its resources into them.
From week 7 onwards you should start checking the trichomes using a magnifying glass or pocket microscope. There should be some noticeable changes to the color as they turn from a clear color to a milky white. This indicates that the plant is almost ready to be harvested. Once the majority of the trichomes have turned milky white your plants are ready to be harvested.
When is the best time to harvest your buds
The color of the trichomes on your plant is a good indicator of when to harvest. Harvesting when the trichomes are mostly clear or translucent will result in a more cerebral, uplifting high, while harvesting when the trichomes are milky or amber will result in a more sedative, relaxing high.
Typically, growers wait until 50-70% of the trichomes have turned milky or amber before harvesting, as this is when the THC levels are at their highest. However, the optimal time to harvest will vary depending on the desired effect and personal preference. Check out our article on how to harvest cannabis for a more detailed discussion.
It is important to monitor the trichome color regularly and harvest at the right time to ensure the highest quality buds. Over-ripe buds can result in a harsh, unpleasant smoking experience and lower THC levels.
Many growers also claim that leaving plants in complete darkness for 48 hours directly before they are harvested increases trichome production resulting in higher THC levels.
The flushing stage
Flushing is the process of removing all of the leftover nutrients that have built up inside the plant before it is harvested. This helps to improve the taste, aroma, and overall quality of the buds, as well as reduce the risk of any chemical or nutrient residue.
If you have grown your weed using organic nutrients then you don’t need to flush your plants. However, most growers that use synthetic nutrients carry out a flush in the final 5-10 days before harvest.
To flush your plants, next time you water them don’t add any nutrients and just feed them with pH adjusted water. This helps to remove excess salts and minerals from the soil and plant so that the buds are free of any residual nutrient taste or odor.
Key best practices for the flowering phase
- Provide adequate light: During the flowering stage, the plants need 12-14 hours of darkness and 10-12 hours of light per day to trigger the flowering response.
- Maintain the right temperature and humidity: Keep the temperature between 68-78°F (20-26°C) and relative humidity between 40-50% to prevent mold and mildew growth on the buds.
- Reduce humidity to 30-40% during the later stages of flowering.
- Monitor the nutrient levels: Provide the correct ratios of nitrogen, phosphorus, and potassium to support healthy bud development and reduce the risk of nutrient deficiencies.
- Regularly check for pests and diseases: Inspect the plants regularly for signs of pests and diseases and treat promptly to prevent any damage to the buds.
- Provide support for the plants: As the buds mature, the plants may start to stretch and become top-heavy, so providing support such as stakes or trellis may be necessary to prevent breakage.
- Flush the plants before harvest: Flushing the soil with plain water before harvest will help to remove any residual nutrient taste or odor and improve the overall quality of the buds.
- Monitor the trichome color: Use a magnifying glass to observe the trichome color and harvest when the desired potency is reached.
How long is the cannabis flowering stage?
The cannabis flowering stage is usually between 6-14 weeks, depending on the strain and if you are growing indoors or outdoors.
- Indica strains tend to flower faster, with a flowering time of 8-9 weeks.
- Sativa strains tend to have a longer flowering time of 9-14 weeks.
- Autoflowers take 6-8 weeks depending on if they are sativa or indica dominant.
- Fast flowering photoperiods normally take 6-9 weeks depending on if they are sativa or indica dominant.
Should you remove fan leaves during the cannabis flowering stage?
Removing fan leaves during the flowering stage is a common practice called defoliation. It can help to improve light penetration and air circulation within the plant canopy, which can in turn promote healthy bud development and increase yield.
Fan leaves are the large, flat leaves that are found at the bottom of the plant and are not directly involved in the production of flowers or buds. Removing these leaves during flowering can help to redirect the plant’s energy and resources towards the buds, making them bigger and more resinous.
However, removing fan leaves should be done carefully and selectively, as they also play a crucial role in photosynthesis, which is the process by which the plant converts light into energy. Removing too many fan leaves can stress the plant and reduce its overall health and yield.
Growers generally remove the yellowing or damaged fan leaves but leave the healthy ones to continue providing energy to the plant. It’s important to evaluate the plant regularly and only remove fan leaves as needed.
Do plants need more water during flowering?
Producing bud is an energy intensive process for cannabis plants and so they require more water during the flowering stage. It’s important to keep the soil consistently moist, but not waterlogged, to prevent stress on the plant and ensure healthy roots. Over-watering can lead to mold and root rot, while under-watering can cause wilting and slow down the growth of the buds. You should not just water cannabis plants because your schedule says so, monitor the soil moisture regularly and adjust the watering frequency based on the feel of it. If the soil is dry to the touch then water your plants, if it is still damp then you can leave watering and check the soil again in another 12 hours.
Tanney et al. (2021) Cannabis Glandular Trichomes: A Cellular Metabolite Factory. Published on Plant Metabolism and Chemodiversity, Volume 12 – 2021. Available at: https://doi.org/10.3389/fpls.2021.721986